WATERLOO, Iowa (AP) — In his rise to the top tier of the Democratic race for president, Pete Buttigieg has impressed voters with his unflappable demeanor. But that moderate bearing is being tested as his opponents challenge him to reveal more about his two years working for an international consulting company.

How Buttigieg handles the heat will be another measure of the durability of his improbable run, now that the mayor of South Bend, Indiana, is seen as a serious threat to front-running candidates, especially in Iowa.

To date, the more intense inspection — much of it invited publicly by rival Elizabeth Warren — doesn’t appear to be slowing Buttigieg’s progress in Iowa, where he’s attracting large, excited crowds. But with more than eight weeks until Iowans march to their caucuses, there is still time for a drumbeat to begin.

“The more heat there is, I welcome that,” Buttigieg told reporters in Waterloo Friday. “We’re talking about the American presidency and you should be able to show you can handle tough decisions, tough questions.”

In the face of new questions about transparency — most notably about his three years with international consulting firm McKinsey & Co. — the South Bend, Indiana, mayor says he is taking steps to provide transparency, though stopping short of revealing the clients he’s legally bound to keep confidential.

The new questions about Buttigieg’s role at McKinsey, including some time spent working in wartime Iraq and Afghanistan, come after his November rise to the top of Democratic preference polls in Iowa and New Hampshire, where voting for the 2020 presidential nomination begins.

After shying away for months from criticizing her rivals by name, Warren, a Massachusetts senator who shot to the top of Iowa polls last summer, has called on Buttigieg to release the names of his McKinsey clients, disclose his campaign’s most influential donors and open his fundraisers to the news media.

Now fighting to catch Buttigieg in Iowa and New Hampshire, Warren has begun mentioning him by name in the context of her campaign’s central theme: ending corporate influence in public policy, especially in light of President Donald Trump’s refusal to release his income tax records.

“We’ve got a chance as Democrats to say we’re going to do this a different way and that different way does not involve going behind closed doors with millionaires and billionaires,” Warren told reporters in New Hampshire Saturday.

The Buttigieg campaign released the names of about two dozen fundraising bundlers for the first quarter in April, but hasn’t since then. Buttigieg has said he would consider naming more and opening fundraising events to public but declined to give a timeline for a decision.

He has released tax information, and given a timeline for his work at McKinsey, describing projects he worked on without naming corporate clients. But Buttigieg declined to declined to say whether he would break the agreement should the firm deny his request to release him.

“Well, then they’re putting me in a difficult position,” he said Saturday.

It’s a first look at how the Cinderella campaign of this onetime asterisk in the Democratic field is responding to his increasing time under the microscope.

The questions appeared to have no impact on Buttigieg’s weekend campaign events, which drew large and excited crowds across Democrat-rich eastern Iowa.

Cathy Ondler of Cedar Rapids, who stood among 1,000 people at tiny Cornell College in Mount Vernon, Iowa, to see Buttigieg Saturday, said he spent little time at McKinsey when he was just out of college, though she was familiar with the questions.

“I don’t think he has anything to hide,” the 44-year-old finance director for a nonprofit group said. Ondler is considering supporting Buttigieg or Minnesota Sen. Amy Klobuchar.

Former state Rep. Nate Willems, a 40-year-old labor lawyer and former state representative from Mount Vernon, doesn’t expect to support Buttigieg, but said, “He’s getting picked apart on Twitter, not among everyday Iowa Democrats.”

Still, Chicago Mayor Lori Lightfoot put Buttigieg on the spot Friday, urging him to break the non-disclosure agreement to send a message in the age of Trump.

“Shouldn’t you break that NDA so that you have the moral authority and the high ground against somebody like Trump, who hides behind the lack of transparency to justify everything that he’s doing?” the Chicago mayor asked Buttigieg during a one-on-one question session at a conference in Waterloo.

“I’m going to give them a chance to do the right thing,” he replied.

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Associated Press writer Hunter Woodall in Rochester, New Hampshire, contributed to this report.

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